Magnetic focusing mechanism



Dec. 29, 1953 S. L. REICHES ETAL MAGNETIC FOCUSING MECHANISM Filed March 10, 1952 16 flzzz/ezzfard A5222 ZZez'c/zey $027022? 71 1229212 Patented Dec. 29, 1953 MAGNETIC FOCUSIN G MECHANISM Sol L. Reiches, Cleveland, and Defiance, Ohio, assignors to Donald Paul Ingle, All Star Products,

Inc., Defiance, Ohio, a corporation of Ohio Application March 10, 1952, Serial No. 275,807

6 Claims.

Our invention relates to an improved magnetic focusing and centering mechanism suitable for use with cathode ray tubes of the type having internal pole pieces. Our invention also relates to a magnetic focusing and centering mechanism including such tube.

Magnetic focusin and centering devices for cathode ray tubes have numerous advantages, but the construction heretofore required has demanded large and powerful-and hence expensive1:ern:anent ma;nets. This arises from the fact that the apertures in the pole pieces must be of size to receive the neck of the tube and yet must produce a magnetic field at the axis of the tube that effectively focuses the ray beam.

Efforts have been made to decrease the size of the required magnets in magnetic focusing devices by using internal annular magnetic poles. Poles so positioned can use apertures only slightly larger than the extent of the actual cathode ray beam positions. The poles are therefore much more effective in focusing the ray beam and smaller, less expensive, magnets are required. Internal magnetic poles, however, have the disadvantage of being immovable. Centering movements available with external focusin and centering devices are accordingly not available.

The present invention relates to an improved external magnetic focusing and centering device which is capable of effectively centering the cathode ray beam despite the immovabiLty of the internal poles mounted in the neck of the tube.

Briefly, the unit of the present invention utiliZes a pair of annular magnetic pole pieces received over the neck of the tube in the region of the internal poles. One of the external pole pieces is out of registration with the corresponding internal pole and carries a universally shiftable slide pole piece. This slide pole, when shifted, varies the centering of the electron ray beam. The intensity of the effective magnetic field is controlled by an external movable shunting sleeve which telescopes over the external pole pieces.

It is therefore a general object of the present invention to provide an improved magnetic focusin; and centering device suitable for use with a cathode ray tube having internal magnetic poles.

Another object of the present invention is to provide an improved cathode ray beam focusing and centering system requiring a minimum magnetic energy and yet achieving efiective focusing and centering action.

Still another object of the present invention is to provide an improved focusing and centering device for a cathode ray tube with internal magnetic poles which device telescopes over the neck of the tube and is of simple and inexpensive construction.

Further it is an object of the present invention to provide an improved focusing and centering device for a cathode ray tube having internal magnetic poles and capable of operating over a large range of axial positions on the neck of the tube.

The novel features which We believe to be characteristic of our invention are set forth with particularlty in the appended claims. Our invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by refercnce to the following description taken in connect'on with the accompanying drawings in which:

Figure l is a view in axial cross-section of the neck of a cathode ray tube having internal magnetic poles with a focusing and centering unit telescoped thereover, all constructed in accordance with the present invention;

Figure 2 is a cross-sectional view through axis 2-2, Figure 1;

Figure 3 is a fragmentary view like Figure l but showing a modified arrangement of the inter nal magnetic poles;

Figure 4 is a cross-sectional view through the axis 44, Figure 1;

Figure 5 is a cross-sectional view through the axi 5-5, Figure 1;

Figure 6 is a fragmentary cross-sectional view through axis 6-6, Figure 2;

Figure '7 is a fragmentary cross-sectional view through axis l-l, Figure 2; and

Figure 8 is a fragmentary cross-sectional view through axis 8-8, Figure 2. 1

Referring now to Figure i, there is shown at N the neck portion of a cathode ray tube. This tube has a cathode ray gun G which produces and accelerates a beam of electrons in a stream substantially coaxial with the neck of the tube and in the direction of arrow A. The neck of the tube has a pair of axially spaced annular magnetic poles P1 and P2 located on the downstream side of the gun In the tube structure of Figure 1, these poles are of simple annular conformation and are of identical construction. Each has a central circular aperture through which the electron beam passes.

The pole pieces P and P2 are of magnetic material such as soft iron. The apertures in the poles are of sufiicient size to obstructing the ray beam and yet are as small as possible to assure most emcient production of the fringing magnetic flux that focuses the ray beam.

The focusing and centering device telescoped over the neck of the tube consists of a pair of annular magnetic pole pieces it! and i2, corresponding, respectively, to internal poles P1 and P2. Three bar-type permanent magnets 14 are sandwiched between the pole pieces Id and H2 at substantially equal circumferential spacings as shown in Figure 5. These magnets are located adjacent the periphery of the poles i8 and 12. As shown in Figure '7, the pole pieces are secured. over the magnets l l by the screws l3. which at their headed ends Hie seat on pole piece it and at their threaded opposite ends are threadedly received in the pole piece la.

The pole piece is has a relatively small internal diameter and forms an extended cylindrical flange lfia, Figure 1, at its inner periphery. This flange extends outboard of the cage formed by the pole pieces l8 and i2 and the magnets i i and in the upstream direction in relation to the cathode ray beam.

The pole piece i2 is or" the same outer diameter as pole piece it but the inner diameter, defined by the aperture 12a, is of larger diameter than the inner periphery of pole piece 55!. A magnet slide pole piece it is mounted on the outboard side of pole i2. It is of annular conformation having a window or aperture We of smaller diameter than the aperture iZa of pole piece 52 and of larger diameter than the inner periphery of pole piece it.

The slide pole i8 is mounted on pole it for universal shifting motions. This is accomplished by rivets 26 which ride in the elongated radial slots 58d of slide pole it. One rivet is in fixed position on th pole piece !2 and the other, diametrically opposed, rides in the elongated arcuate circumferentially extending slot its of the pole piece l2, as shown 2. As a result, the slide pole may be shifted universally to a desired position in relation to the fixed pole piece l2.

An operating handle idb extends outboard of the slide pole iii to facilitate adjustments thereof. This handle, and hence the pole 58, may be adjusted by suitable mechanical means (not shown) to vary the position of the slide pole ii on the fixed pole 12.

The fixed poles iii and i2 and the slide pole [8 are or" any suitable magnetic material, such as mild. steel.

The intensity of the magnetic flux between the internal portions of the pole pieces it and I2 is controlled by the adjustable magnetic shunting sleeve 22. As shown in Figure 8, this sleeve has an inturned tab 22a to which is secured a threaded stud 2d. The latter extends through an appropriate opening in the pole piece it} and telescopes within the fixed axially extending sleeve 26, mounted thereon. A cap 28 threadedly receives the stud and seats against the outer end of thev sleeve 26. A conical spring 38 seats against the tab 22a, and pole piece it to hold thetab, and hence the shunting sleeve :22, at the maximum spacing permitted by the adjustment of cap 28.

The sleeve '22 is of magnetic material, such as mild steel. Consequently, as the cap 28 is rotated,

and the axial position of the sleeve 22 correspondingly varied, the sleeve 22 shunts a controllable.

quantity of magnetic flux between pole pieces it. and 92. This flux is subtracted from the substantial constant total flux created by the magnets so.

that the field between the pole, pieces, It. and i2,

and hence the apparent magnetomotive force thereacross, is varied.

The sleeve 22 is held in centered position by the tab 221), Figure 6. This tab is generally like tab 22a but is circumferentially spaced therefrom as shown in Figures 4 and 5. The tab 22b has an aperture through which a fixed pin ll? of the pole piece 19 extends to anchor the tab while permitting axial sliding motions of the sleeve 22.

It will be noted that the slide pole I5 is located at a position out of axial registration with, and substantially downstream of, the corresponding internal pole P2, as shown in Figure 1. In other words, slide pole is is axially outboard of the internal pole P2. It has been found that with the slide pole is, and the fixed pole E2, in these positions in relation to internal pole piece P2, motions of the slide pole effect centering motions of the cathode ray beam. If the slide pole i8 and fixed pole ii are in alignment with the fixed internal pole P2, it has been found that motions of the slide pole are not effective in centering the oathode ray beam.

The flange Hm registers with the internal pole piece P1 over a wide range of positions of the external focusing and centering unit. Consequently, the position of the external unit is not critical since the effective air gap reluctance between pole P1 and pole piece it is substantially constant over a variety of axial positions.

Figure 2 shows a modified form of the internal pole piece P1. In bhiS structure pole piece P101 corresponds to pole piece Pi but differs therefrom in having a conical portion extending downstream of the electron beam and towards the internal pole P2. The external structure used with this pole arrangement is the same as that shown in Figures 1, 2, and 3 to 8.

The apparatus of the present invention has proven highly successful in focusing and centering the cathode ray beam by the use of relatively weak and small energizing magnets. While the internal poles are in fixed position, and hence would appear to preclude beam-centering adjustments, it has been found that in actual practice shifting movements of the slide pole 18 give an adequate degree of centering motion.

It will be observed that the pole pieces l0 and [2 are spaced a sufficient distance. so that with the pole iii overlying, or in registration with, the pole P1 (or P101, Figure 3),, the poles l2 and I8 are outboard of the downstream internal pole P2. In other words, the pole pieces Ill and I2 have a greater spacing than the poles P or F2 or, in the case of Figure 3, poles P101 and P2.

The flange Hit: of the pole piece in projects outwardly and rearwardly, as seen in Figure l, bacuse the length of the magnets id is relative ly short. If magnets is are longer than the spacing of poles F1 and P2, thev flange Illa can. be turned inwardly and forwardly, as seen in Figure 1, to provide registration with the internal poles P1 and P2 over a substantial range of positions of the unit.

In the appended claims we have referred to the. outboard edge of the cylindrical flange Ifia as the edge outboard of the cage defined by pole pieces l6 and it. In other words, this is the upstream edge of the flange with respect to the direction of electron flow in Figure 1.

While we have shown and described specific embodiments of the present invention, it will be understood that many alternative embodiments may be, made without departing from the true spirit and scope thereof. We therefore in.-

tend by the appended claims to cover all such modifications and alternative constructions falling within their true spirit and scope.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A magnetic focusing device for a cathode ray tube having a neck within which are mounted a pair of spaced internal magnetic poles, the focusing device comprising; a pair of spaced annular magnetic pole pieces, magnets sandwiched between the pole pieces and sustaining the same in spaced positions, one of the annular magnetic pole pieces having an aperture substantially the size of the neck of the tube and an inner cylindrical flange, the other of the annular magnetic pole pieces having an aperture substantially larger than the neck of the tube, the annular magnetic pieces being spaced so that when said inner cylindrical flange is in registry with one internal pole said other annular magnetic pole piece is outboard the other internal pole, and a slide pole piece mounted on said other pole piece for universal sliding movement and having an aperture smaller than the aperture of said one pole piece.

2. A magnetic focusing device for a cathode ray tube having a neck portion within which are mounted a pair of spaced internal poles, the focusing device comprising; a pair of spaced annular magnetic pole pieces, magnets sandwiched between the pole pieces and sustaining the same in spaced position, one of the annular magnetic pole pieces having an aperture substantially the size of the neck of the tube and an inner cylindrical flange having outboard and inboard edges, the other of the annular magnetic pole pieces having an aperture substantially larger than the neck of the tube, the annular magnetic pole pieces being spaced So that when said inner cylindrical flange is in registration with one internal pole said other annular magnetic pole piece is outboard the other internal pole, a slide pole piece mounted on said other pole piece for universal sliding movement and having an aperture smaller than the aperture of said one pole piece, and a magnetic sleeve in telescopic relation with the annular magnetic pole pieces for axial field adjusting motions.

3. In combination, a cathode ray tube having a neck, first and second internal magnetic poles in the neck of the tube, first and second annular magnetic pole pieces external to the neck of the tube, the first external pole piece having an aperture substantially the size of the neck of the tube and being located in substantial registration with the first internal pole, the second external pole piece having an aperture substantially larger than the neck of the tube and being located in spaced relation to the second internal pole, a slide pole piece mounted on the second external pole piece for universal sliding movement and having an aperture smaller than the second external pole piece, and magnets sandwiched between the external pole pieces.

4. In combination, a cathode ray tube having a neck, first and second internal annular magnetic poles in the neck of the tube at axially spaced positions, first and second annular magnetic pole pieces external to the neck of the tube, the first external pole piece having an aperture substantially the size of the neck of the tube and being located in substantial registration with the first internal pole, the second external pole piece having an aperture substantially larger than the neck of the tube and being located in axially outboard relation to the second internal pole, a slide pole piece mounted on the second external pole piece for universal sliding movement and having aperture smaller than the second external pole piece, and magnets sandwiched between the external pole pieces.

5. In combination, a cathode ray tube having a neck, first and second internal magnetic poles in the neck of the tube, first and second annular magnetic pole pieces external to the neck of the tube, the first external pole piece having an aperture substantially the size of the neck of the tube and a cylindrical internal flange, said pole piece being located with the flange in registration with the first internal pole, the second external pole piece having an aperture substantially larger than the neck of the tube and being located in axially spaced relation to the second internal pole, a slide pole piece mounted on the second external pole piece for universal sliding movement and having an aperture smaller than the second external pole piece, and magnets sandwiched between the external pole pieces.

6. In combination, a cathode ray tube having a neck, first and second internal magnetic poles in the neck of the tube, first and second annular magnetic pole pieces external to the neck of the tube, the first external pole piece having an aperture substantially the size of the neck of the tube and a cylindrical internal flange, said pole piece being located with the flange in registration with the first internal pole, the second external pole having an aperture substantially larger than the neck of the tube and being located in axially spaced relation to the second internal pole, a slide pole piece mounted on the second external pole piece for universal sliding movement and having an aperture smaller than the second external pole piece, magnets sandwiched between the external pole pieces, and an axially slidable magnetic shunt in telescopic relation to the external magnetic pole pieces.

SOL L. REICHES. D. PAUL INGLE.

References Cited in the file of this patent UNITED STATES PATENTS Schiel et al. Jan. 1, 1952 

